(a) Structure of exosome depicting the molecular components; the phospholipid bilayer (blue colored) encloses the vesicle. Internally, the vesicle consists of cargo comprising nucleic acids, proteins, and lipids.

(b) The biogenesis of exosomes involves (1) cargo from the extracellular space entering the cytosol through internalization wherein it forms the early endosome. (2) Early endosomes mature to form multivesicular bodies (MVBs) consisting of intraluminal vesicles that include tetraspanin (CD9, CD63, and CD81), an endosomal sorting complex required for transport (ESCRT) proteins (Alix, TSG101), integrins, heat shock proteins, cytoskeletal proteins, and membrane transport proteins. (3) Cargo internalization consists of cargo delivery from the trans-Golgi network and the cytosol. (4) MVBs consisting of exosome cargo are transported to the plasma membrane (PM) with the help of a microtubule network and Rab GTPases. (5) SNAREs dock the MVBs to the PM and ILVs are secreted as exosomes.